"Since the test was officially announced recently, our core developers have been hard at work fixing bugs and adding the missing standards support. Today we reached a 100% pass rate for the first time! There are some remaining issues yet to be fixed, but we hope to have those sorted out shortly."

Opera and Safari (and Firefox, for that matter) have to concern themselves with a heck of a lot of regression testing before they can release a final version with Acid3 support. It's one thing to have features implemented 100%, it's another to break 10% of all websites in doing so.

Unfortunately, the smaller the market share, like Safari and Opera, the greater the number of poorly-tested hacks are out there in the wild.